The United States Adopted Names (USAN) Council’s goal is to provide meaningful designations for compounds, enhancing prescribing and patient safety. Excessive stem creation diminishes the usefulness of the system. The council strives to use existing stems whenever possible. The burden of proof falls on the applicant to show assignment of a new stem is warranted. In the opinion of the council, a new stem may be selected if substantial data shows a substance is unique and cannot fit existing nomenclature.
Using stems
The listing of USAN stems (XLSX) represents common stems for which chemical and/or pharmacologic parameters have been established. These council-approved stems and their definitions are recommended for use in coining new nonproprietary drug names belonging to an established series of related agents.
USAN appropriately incorporates existing stems in the names of new compounds receiving a new USAN. By doing so, similar compounds maintain a common "family" name that provides immediate recognition.
The list is not exhaustive. It does not include all stems used by the council and other national or international nomenclature groups. The nature of the nomenclature process is that new potential stems are constantly being created and that definitions of older stems may need to be modified as new information becomes available.
The following document contains new USAN stems that received official approval at recent USAN Council meetings: Newly approved in June 2026 (PDF).
